Alcohol may be good for your heart in moderation, but drinking as little as half a glass of wine a day may raise a woman's risk of developing breast cancer, a new study shows.

And don't think that switching to beer or spirits is the answer: The more alcohol consumed on a regular basis, the greater the risk, says Wendy Y. Chen, MD, PhD, a cancer specialist at the Dana-Farber Cancer Institute in Boston.

The study was presented at the annual meeting of the American Society of Clinical Oncology.

Chen notes that women thinking about having a few glasses of wine a day for their heart-healthy effects need to figure in the new findings when weighing the risks and benefits.

She stresses that "its only regular, repeated use that increases the chance of breast cancer. For most women, having a glass of wine or beer on occasion is not a problem."

Postmenopausal Women at Greatest Risk

Previous studies have linked alcohol intake with an increased breast cancer risk. Alcohol may change the way the body metabolizes estrogen. Many breast cancers are fueled by the hormone estrogen. Therefore, regular use of alcohol is thought to increase the risk of breast cancer by increasing blood estrogen levels.

The new study tracked the health of 122,000 women since 1976. They were free of cancer at the start of the study. Every four years, the women were asked how much alcohol they had used during an average month in the past year.

By 2002, nearly 6,000 of the women developed breast cancer.

When compared with teetotalers:

Women who drank the equivalent of a half glass of wine a day were 6 percent more likely to develop breast cancer.
Women who drank a glass or two a day faced a 21 percent increased risk of breast cancer.
Those who drank more than two drinks a day were 37 percent more likely to develop breast cancer.
However, the risk was much greater in menopausal women:

Menopausal women who drank a half glass of wine daily increased their chance of breast cancer by 18 percent.
The elevated risk was also more pronounced for women whose tumor growth was fueled by the hormones estrogen or progesterone -- a group that accounts for about 70 percent of women with breast cancer.

Assessing Breast Cancer Risk

The American Cancer Society lists alcohol as a risk factor for breast cancer. It clearly states that having a drink or more a day is a risk factor for the disease. One standard drink a day is defined as moderation for women.

But this is the first study to show that even a half glass a day is associated with "a slight but definite increase in risk," says Len Lichtenfeld, MD, the society's deputy chief medical officer.

So what should a woman do with all this new information?

First of all, don't fret if you've indulged in a glass of wine or beer now and then, Chen says.

At the same time, don't think that abstaining all week only to start partying come happy hour on Friday is going to help, Chen tells WebMD. "It's the average amount the counts -- a glass a day for seven days carries the same risk as seven glasses on one day, once a week."

Also, don't make the mistake of thinking that becoming a teetotaler means you'll lower your risk of the disease, Lichtenfeld says.

The new findings "have to be looked at as one more piece of information among many risk factors," he tells WebMD. "In the big scheme of things; [alcohol] is a small issue" compared with something such as family history."

A sure bet: Follow a healthy lifestyle, with a good diet, exercise, and avoidance of smoking and heavy drinking, Lichtenfeld says.

By Charlene Laino, reviewed by Brunilda Nazario, MD

SOURCES: 41st Annual Meeting of the American Society of Clinical Oncology, Orlando, Fla., May 13-17, 2005. Wendy Chen, MD, PhD, instructor in medicine, Harvard Medical School, Dana-Farber Cancer Institute, Boston. Len Lichtenfeld, MD, deputy chief medical officer, American Cancer Society, Atlanta.